It's not behind a paywall, so I think I can reproduce it in its entirety
here (go read New Scientist anyway). In general I'm pretty pleased with it,
although there's one point I'd like to explore: "In
reality, climate change is unlikely to have a single catastrophic point of
failure, and might, to stretch the analogy, be a series of increasingly severe
drops."

Here's the problem with the analogy, and with 'targets' in general. The
waterfall is a binary outcome, increases in temperature are not. 1.6 degrees is
not the same as 3.6. A better analogy here would be a series of rapids (I like
white water canoeing by the way. Go Team 'Stupid Geese'). One might imagine
that the start of the rapids are gentler and, that for the first few seconds we
might be able to paddle upstream and get to the bank. This is actually a better
analogy for greenhouse gas removal, it may return us to safety even after we've
overshot. Every metre we travel into the rapids the further we've got to paddle
back and, importantly, the more severe the outcome. Is this a problem inherent
with targets? Maybe so. Does missing 1.5 mean anything politically. Will it
generate political apathy? or galvanise the political classes. Who knows? I
suspect an aspirational target is, overall, a net positive but without
addressing how we might stay below 1.5 it is fairly meaningless.
I've applied to be a lead author on the IPCC 1.5 degree report. I'd be very
surprised if anyone associated with SRM gets selected, so politically toxic is
the idea. That, unfortunately, is going to have to change...

_________

The Paris climate agreement’s goal of stopping the world warming more than 1.5 °C produced a strong but mixed response from scientists. While most welcomed its intention, and the marker it put down, some, including me, were also alarmed,wondering how that goal might be achieved. Here’s the truth, made all the more plain by thepossible withdrawal of the US from the Paris agreement: if we wish to stay below 1.5 °C we have to deliberately intervene in the global climate system on a massive scale. Nothing of that scope has ever been attempted. The worst implications of a warmer world –sea-level rise, crop failure and population displacement – would make it immoral not to act if we can. These potential impacts look much less far-fetched than they did even a decade ago. We are nearing the point at which we must act. Hence the growing call for a full and frank discussion of allgeoengineering methods. These would aim to alter the planet’s radiation budget, for example, by pumping reflective or cloud-altering particles into the air. In particular,field trials of radiation management (RM) methods to cool the Earth now need immediate support.

Why the urgency? Because we are in a raft without paddles heading towards a waterfall and we’re running out of options. We could paddle for the bank with our hands. That’s like curbing carbon emissions and requires co-operation and leadership. But we’ve left it too late – we’re too near the waterfall to make it to safety this way. We could build makeshift paddles to row quicker. This is like greenhouse gas removal, the development of technologies that suck carbon dioxide out of the air – so-callednegative emissions. But it looks doubtful we can make the paddles in time. Or we could brace ourselves for the inevitable, strap ourselves in and those that have them might put on hard hats in the hope they are sufficient. This is adaptation, like bolstering coastal defences or relocating threatened populations and letting the waters rise.Alternatively, we could swim for it. But that’s risky as the water looks cold and not everyone can swim. This is like using radiation management. You can do this quickly and relatively cheaply but the outcome is less certain. This option, given its potential for rapid deployment,has been woefully under-researched.

The waterfall analogy highlights the importance of information. If we knew how long we have before we fall over the waterfall, the severity of the fall, the amount of time it would take to make a paddle and the temperature and depth of the water you could make a more informed decision. More geoengineering research will give us more information. Fortunately, these options are not mutually exclusive. In reality, climate change is unlikely to have a single catastrophic point of failure, and might, to stretch the analogy, be a series of increasingly severe drops. Of course it makes sense to properly explore all options – continue to wean ourselves off carbon, develop negative emissions technologies and brace for the impacts of climate change. But we must also “test the water” in case we decide to swim for it. That means considering properly, through research and a more open and honest discussion, the unpalatable choice of climate engineering through radiation management.

I should say that I like Erik, and his blog,
a lot (full disclosure, we've never actually met) but felt much of this article
was wrong. Also, as an aside and for some context, we recently had something of
a polite disagreement on the terms of engaging with the media around this article:

I was tempted to write something back to this, but
went on holiday instead. Short version: it's worth engaging with media, I made
the article better, there's no simple way to get the article you want - your
only option is simply not to engage. I proved this to myself when dealing with
a different journalist, at the same paper, on a second story a week later (on
Iceland).

In that case, I insisted on more editorial control, thinking most
whilst people would appreciate that every volcano erupting at the same time was simply
a thought experiment, taking about likelhood of eruptions in Iceland was
pretty serious. I got short shrift from the editor. Fortunately, the piece was mostly
sensible (except the headline) and they got volcanologists with much greater
expertise than me to provide quotes.

So it's either engage at your own risk or don't (or
write a hugely popular blog).

Anyway, now that's out of the way, let's get onto
the 2012 article. Here it, is - as always my comments in red:

I’VE
SEEN A number of articles in the news recently touting [subtly implies 'for gain' which is not at all fair, maybe I'm overly sensitive!] the idea that man-made volcanoes could help mitigate against heat waves on a
local scale. On the surface, that seems like a great idea … and I know, with
Ohio gripped in what seems like an endless parade of >90ºF degree days this
summer, even the suggestion that there might be a way to cool the region when
the heat hits seems too good to be true. Well, you know how the saying goes,
and sure enough, building an artificial volcano is not going to solve the
ever-increasing problems with a warming planet. How
do you know that, so little research has been done? An unqualified sweeping
statement.

Here is the idea – when a volcanic eruption occurs, thousands [at least]of tonnes of material are thrown into
the atmosphere. This material comes in a number of flavors. A lot of it is
water vapor, usually from water that was dissolved in the magma and is now
being released when the bubbles in the magma pop, causing an explosive
eruption. Another large component of the material is ash fragments – these fragments are volcanic glass,
mineral grains and fragments of pulverized rocks from previous eruptions that
get caught in the action. The water vapor and ash can cause changes in the
atmosphere, especially near the volcano where light can be totally blocked when
the eruption is in full swing and the ash clogs the air. However, when we’re
looking at the impact a volcanic eruption can have on weather and climate, the
components that are most important are the
aerosols (when in droplet form) – carbon dioxide (usually
a gas), sulfur dioxide, hydrogen sulfide, fluorine, chlorine and more. The
first three are the biggies as they can promote both heating and cooling of the
atmosphere, with CO2 mostly driving warming
(via greenhouse) and SO2/H2S driving cooling by dispersing the energy of the
sun before it reaches the surface. [This
is pretty confusing. All of the species listed are gases. Better to talk about
them (as gases) being disolved in water (which dropped off the list?) or, in the case of
sulphates, the solid phase too. This matters as CO2 (gas)
has a warming effect but gases in solution (most notably SO2 of course) are the climate coolers. The emitted gases are precursors to the aerosol].

The big, sulfur-rich eruptions are the ones that
seem to have the biggest effect on the global climate. You think of eruptions
like Pinatubo (1991), El Chichon (1982), Laki (1783), Tambora (1815) and more – these really made a mark on global climate, usually causing cooling across
hemisphere and potentially causing increased rain or droughts as regional rain
patterns changed. Some, however, did also cause increasing temperature, as the
dry fogs associated with Laki seem to coincident with a very hot summer across
Europe. So, although most of the effect is cooling, it isn’t the only effect. [Warming was also measured in Northern Europe during NH winters after Pinatubo].

Geoengineers submitted to Atmospheric Chemistry and
Physics that producing a small artificial
volcano that spits aerosolized sulfur compounds into the
atmosphere, we can decrease the amount of solar radiation reaching the Earthon a
localized level, thus cooling that area. Sure, in theory, that is exactly what
should happen. A number of problems exist: (1) the cost of the technology to do
this is very high, [no it isn't. In fact, it's frighteningly
cheap. I suspect it's > 1000 x cheaper than mitigation or adaptation. That
gearing could be much higher, and might make geoengineering 'tempting'. The real cost of geoengineering would be around
impacts, the technology itself is very, very cheap. So cheap
individual rogue actors could (in principle, not saying it's particularly likely) deploy the technology] (2) some of the technology doesn’t exist yet [yes it does, we could do this in only a few years (or quicker on a
Manhattan project-like footing)] and
(3) we don’t know what we’re doing [yet
you've just provided a detailed description of what happened after Laki (and we
know far more about the response from Pinatubo). Do we know everything? No. Can
we predict first order effects, for 'peak shaving' (argument is more
complicated, see below), yes]. Sure, #1 and 2 can
be overcome, but #3 is the most troubling – although we might be able to engineer this artificial volcano, we surely
don’t understand the greater effects and long-term
consequences of action like this. This
is why more research is needed, particulary around the next VEI6 eruption.

This
next section sounds compelling but is a total red herring. It's comparing
uncontrolled release into the lower troposphere with controlled stratospheric
injection. This is exactly the same mistake George Monbiot made when
criticising geoengineering. Did Pinatubo affect the Midwest? Nope. Are people
seriously proposing pumping the amount of material that industry did in the
70's and 80's. Nope. Most researchers are looking at slow ramping up of
injection, starting at as little as 50,000 tonnes a year, to slow down the rate
of warming in a controlled manner (called peak shaving).

Let’s still back and think back to the 1970’s and
80’s. What was a big problem across much of the Midwest and the eastern
U.S.? Acid rain! How is acid rain formed? By pumping a whole
bunch of aerosolized sulfur (and other goodies) into the atmosphere. At that
time, it was not to cool the climate, but rather from the thousands of
factories across middle America. As those factory exhaust fumes spread into the
atmosphere, the jet stream carried the material east, mixed with rain water and produced acidic rains.
This idea of an artificial volcano is really creating the same thing with the
sole purpose of emitting these aerosols. So, you might get a cooler summer, but
downwind they might get a healthy dose of acid rain.

These are
local effects, seen when pumping acids (in hugely high concentrations) into the
lower troposphere (i.e. < 100 m, the height of a chimney, above the surface). The key points are that the aerosols in the stratosphere (> 20 km in the case of aerosol injection) do not behave this way and that (for the example below) anthropogenic emissions into the troposphere vastly exceed (by a factor of 1000) our hypothetical release. There are lots of reasons to dislike this form of geoengineering. Acid rain
is the least of them. I'm much more worried about how little material is requried to have a climatological signature.

Here's a quick calculation. Let's say we release 0.1 Mt
(100, 000 tonnes) a year into the stratosphere and it distributes globally through
atmospheric circulation. If it then fell out from a homogeneous distribution
(clearly not correct, but for a well-mixed atmosphere not as poor an assumption as you might think) we can simply divide by the area
of the Earth to roughly estimate fallout rates. 100, 000, 000, 000 grams (g) /
510, 000, 000, 000, 000 per square metre. (i.e 0.1 g for about a football pitch sized piece of
the Earth per year).

Secondly, we can look at this a lot like the phenomenon of the global use of air conditioners. As more and more people
worldwide take an air conditioned environment as a right, air conditioning
increases without a thought to what the ramifications of all those air
conditioners might be. If you’re one person buying an air conditioner, then it
might not seem to be a big deal (see also: your car), but add up those AC’s,
and the problem gets bigger. Now, picture community after community getting its
own artificial volcano. Who is to stop every town in India or Kansas from
getting one and running it all summer to keep the summer heat down? Now, we’re
no longer talking after micro-volcanoes, but rather likely the equivalent to
several VEI 6+ eruptions from a single country (or state) each
year. What is that going to do to the global climate? We don’t know (other
than, you know, bad things). There is a reasonable
point here, under the ridiculous strawman (effects are not local (c/f above discussion and where did several VEI6+ eruptions
from every country (i.e 50 Mt / yr) come from???). Who has control, and how it
is agreed (or not) what the 'desired' climate looks like is an incredible political
challenge. Given we know what the right answer is (reducing carbon use) and
we're not getting far with that, what chance do we have of implementing what is
obviously a sub-optimal solution? (credit to Peter Irvine for that question).

Humans
have solved many of their problems throughout history through technology –
we’re good at it. We’re also good at overlooking the long term ramifications of
those technologies – and that is one of the key aspects most ideas like this
overlook: human nature and behavior. This point is
both annoying and patronising. No-one, even the most positive about
geoengineering never, I say it again, NEVER, considers
these problem without thinking about 'human nature and behaviour' (we'd call it
the socio-political context). In fact, that's all we do. We talk about justice,
we talk about governance, we talk about responsibility.

That is how we got ourselves to where we are now. Even geoengineers who [are almost always passionate environmentalists and often distinguised climate scientists] proposed these artificial volcanoes [therefore unsuprisingly] say that the best solution to cooling the
climate is limiting anthropogenic CO2 emissions to help
slow the increasing concentration of greenhouse gases in the atmosphere. We all
know that volcanoes aren’t the cause of global warming, but we should also be aware that
building our own volcanoes won’t be the solution either – at least not without
ramifications we can’t anticipate, at least some of
which will be social/political.

That is not to say there won't be physical
ramifications (most notably, I believe, around rainfall patterns) but these
must be considered in the context of future climate change. There is a range of
future scenarios where it would be immoral not to intervene. We are therefore
beholden to undertake research, on the understanding of a simple premise. Very few serious researchers are strongly in favour of
deployment. Most, like me, would see it as tragedy; nothing less than a total
abdication of our responsibility of planetary stewardship, were we to actually
get to the point where deployment of global climate-altering technology was
deemed necessary.